1. Field of the Invention
The invention generally relates to a projection technology, and also to a projection device and a luminance control method of a projection image thereof.
2. Description of Related Art
Projection devices may project an image onto a large screen to facilitate more people to watch the content displayed on the screen concurrently. Therefore, projection devices are generally used in public places, such as in companies and schools. Further, as large-scale home display products are the trend, projection devices are widely used in general families and also become a common electronic product in people's daily life.
In a display device, the contrast ratio of a frame has a significant impact on the quality of the frame. Therefore, manufacturers work diligently on enhancing the contrast ratio of a projection device. One approach on raising the contrast ratio of a frame is by configuring an aperture mechanism in front of the projection lens of the projection device to control the light emitting quantity. Alternatively, the luminance of the projection light of the projection device is adjusted to enhance the contrast ratio of a frame.
Generally speaking, if a projection device applies a dynamic contrast technique to enhance the dynamic contrast, the power of the projection light source is adjusted according to the different degrees of light field and dark field. However, limited by global image detection, when a light spot or a brighter object appears in an image, even the background of the image is completely black, the luminance of the light source is raised due to the appearance of the light spot and the brighter object. Ultimately, the color purity of the black background is unable to be maintained by reducing the luminance of the light source.
The U.S. Pat. No. 8,232,956 discloses a displayable video with a display definition, wherein the display definition is applicable to the type of the video content to be displayed. The liquid crystal display device controls the luminance of the backlight light source according to the average picture level (APL) measured by an APL measuring portion. When the liquid crystal device is executing the on-screen display (OSD), the range of APL of the measured video signal is determined by the luminance level of the video signal or the genre information included in the inputted video signal or the OSD display information. The upper and the lower non-video areas are deleted and an effective video area is determined. Accordingly, the additional information is displayed when the video signal belongs to a specific genre and the additional information displayed by OSD is excluded. Further, the luminance of the backlight light source is controlled to achieve a display definition suitable for the video signal.
Taiwan patent number 1342155 discloses methods for processing image signals, method displaying image signals, and related devices. The proposed method includes performing a predetermined detection on an image signal; partitioning a frame corresponding to the image signal into a plurality of image areas, wherein each image area includes a plurality of pixels; respectively computing statistic data for each of the plurality of areas according to the results of the predetermined detection to obtain a plurality of statistic data corresponding to the plurality of image areas.